Multi-Gene Phylogeny of the Ciliate Genus Trachelostyla (Ciliophora, Hypotrichia), With Integrative Description of Two Species, Trachelostyla multinucleata Spec. nov. and T. pediculiformis (Cohn, 1866).

Tengyue Zhang,Chen Shao,Saleh A Al-Farraj,Weibo Song,Peter Vd’Ačný,Yurui Wang,Tengteng Zhang

doi:10.3389/fmicb.2021.775570

Abstract

Many hypotrich genera, including Trachelostyla, are taxonomically challenging and in a need of integrative revision. Using morphological data, molecular phylogenetic analyses, and internal transcribed spacer 2 (ITS2) secondary structures, we attempt to cast more light on species relationships within the genus Trachelostyla. The present multifaceted approach reveals that (1) a large-sized species with numerous macronuclear nodules, isolated from sandy littoral sediments in southern China, is new to science and is endowed here with a name, T. multinucleata spec. nov.; (2) two other Chinese populations previously identified as T. pediculiformis represent undescribed species; and (3) multigene phylogeny is more robust than single-gene trees, recovering the monophyly of the genus Trachelostyla with high bootstrap frequency. Additionally, ITS2 secondary structures and the presence of compensatory base changes in helices A and B indicate the presence of four distinct taxa within the molecularly studied members of the genus Trachelostyla. Molecular data are more suitable for delimitation of Trachelostyla species than morphological characters as interspecific pairwise genetic distances of small subunit (18S) rDNA, ITS1-5.8S-ITS2, and large subunit (28S) rDNA sequences do not overlap, whereas ranges of multiple morphometric features might transcend species boundaries.

Highlights

Ciliates are a large group of unicellular eukaryotes with various lifestyles, including endosymbiotic, epibiotic, and free-living (Van As and Basson, 2004; Bai et al, 2020; Wu et al, 2020; Foissner and Berger, 2021; Zhao et al, 2021)
The pairwise Gower’s similarity matrix served as an input for the metric multidimensional scaling (MDS), which was conducted with the help of the SMACOF algorithm and the scikit-learn ver. 1.0 package1 (Pedregosa et al, 2011)
Our new species undoubtedly belongs to the genus Trachelostyla as documented by the nonspirally twisted and elongated body with a conspicuously narrowed peristomial region, the 11:2:5:3 cirral pattern (i.e., 11 cirri in the frontal region, two pretransverse cirri, five transverse cirri, and three caudal cirri), and the Gonostomum-like oral apparatus

Summary

Introduction

Ciliates (phylum Ciliophora Doflein, 1901) are a large group of unicellular eukaryotes with various lifestyles, including endosymbiotic, epibiotic, and free-living (Van As and Basson, 2004; Bai et al, 2020; Wu et al, 2020; Foissner and Berger, 2021; Zhao et al, 2021). Distinguishing Trachelostyla species is difficult because the proposed taxa have a rather similar body size and shape as well as overlapping numbers of macronuclear nodules. This genus was introduced by Kahl (1932) and originally included two species, namely, T. pediculiformis (Cohn, 1866) and T. caudata Kahl, 1932. Borror (1972) made the genus name available by fixing T. pediculiformis as the type species (Berger, 1999; Aescht, 2001). Due to the lack of type locality and information on some taxonomically important morphological features, Gong et al (2006) neotypified T. pediculiformis and revised the diagnosis of Trachelostyla

Methods

Results

Conclusion